Method for inhibiting generation of nitrosodimethylamine in process of treating unsymmetrical dimethylhydrazine wastewater by ozone

Abstract

The invention provides a method for inhibiting generation of nitrosodimethylamine in the process of treating unsymmetrical dimethylhydrazine wastewater by ozone, and solves the problems that nitrosodimethylamine is easy to generate and difficult to thoroughly remove in the existing process of treating unsymmetrical dimethylhydrazine wastewater by ozone, and the pollution risk of large residual volume exists. The method specifically comprises the following steps: 1) controlling the concentration of unsymmetrical dimethylhydrazine in the wastewater to be 80-100mg / L, then adding a catalytic amount of manganese sulfate, and uniformly stirring; (2) adjusting the pH value of the wastewater obtained in the step (1) to 7-9, introducing ozone which is 6-8 times of the theoretical ozone dosage for complete degradation of unsymmetrical dimethylhydrazine into the wastewater, carrying out stirring reaction, continuously introducing ozone into the wastewater until the ozone content is 6-8 times of the theoretical ozone dosage for complete degradation of unsymmetrical dimethylhydrazine when the ozone content is reduced to 1 / 5 of the initial ozone content during the reaction, and continuously carrying out stirring reaction until the ozone content is reduced to 1 / 5 of the initial ozone content; the by-products in the wastewater are completely removed.

Description

A method for suppressing the formation of nitrosodimethylamine during ozone treatment of unsymmetrical dimethylhydrazine wastewater Technical Field

[0001] This invention belongs to the field of liquid propellant unsymmetrical dimethylhydrazine (UDMH) wastewater treatment technology, specifically relating to a method for inhibiting the formation of nitrosodimethylamine during ozone treatment of UDMH wastewater, i.e., a method for controlling nitrosodimethylamine pollution during UDMH wastewater treatment. Background Technology

[0002] Unsymmetrical dimethylhydrazine (UDMH), a liquid propellant, is widely used in spacecraft orbital and attitude control engine systems due to its unique advantages such as high specific impulse, spontaneous combustion, and ease of storage; currently, there is no ideal substitute. However, the production, storage, transfer, loading, transportation, testing, and space launch of UDMH generate large amounts of UDMH wastewater and exhaust gases. If these pollutants are discharged directly without effective treatment, they will inevitably migrate and transform in water bodies, the atmosphere, and soil, posing a serious threat to human health and environmental safety.

[0003] The high toxicity of UDMH wastewater and exhaust gases has been a concern since the 1870s. After years of development, significant progress has been made in detection and treatment technologies, with my country primarily focusing on controlling degradation efficiency, chemical oxygen demand (COD), and formaldehyde levels. Currently, the most promising treatment technology is the ozone / catalyst co-process, which can bring various indicators of UDMH wastewater up to emission standards. However, insufficient attention has been paid to the pollution problem of N-nitrosodimethylamine (NDMA), a potentially potent carcinogen. In recent years, NDMA has attracted global attention due to its strong carcinogenicity. The World Health Organization (WHO) and many countries have set limits for NDMA in drinking water: the WHO's Guidelines for Drinking-water Quality (4th Edition) sets the limit at 100 ng / L, while Canada, Australia, and Massachusetts and California in the United States have set the limit at 40 ng / L. my country's Standards for Drinking Water Quality (GB 5749-2022) has adjusted the water quality reference indicators from 28 in GB5749-2006 to 55, including NDMA, with a limit of 100 ng / L. However, the discharge standards for UDMH wastewater still do not include NDMA-related standards, which means that the potential water pollution risk from NDMA urgently needs to be addressed.

[0004] NDMA is difficult to remove using conventional water treatment processes due to its low Henry's Law constant and octanol / water partition coefficient. Currently, the most effective removal process is ultraviolet (UV) photodegradation, but this suffers from high energy consumption and the easy regeneration of NDMA from photolysis products after chlorination. Therefore, controlling NDMA formation at its source is more economical and efficient. Ozone is widely used for waste treatment due to its ease of operation and low cost; however, studies have found that ozone oxidation of UDMH and its wastewater treatment or natural oxidation products (such as metahydrazone and tetramethyltetraazene) results in molar conversion rates of NDMA as high as 90%, 80%, and 29%, respectively. This indicates that inhibiting the formation of nitrosodimethylamine at its source is crucial, but related research remains relatively scarce.

[0005] Therefore, this invention explores a method to suppress the formation of nitrosodimethylamine during ozone treatment of unsymmetrical dimethylhydrazine wastewater at its source. Summary of the Invention

[0006] To address the problem that existing ozone treatment processes for unsymmetrical dimethylhydrazine (UDMH) wastewater easily generate nitrosodimethylamine (NDMA) which is difficult to completely remove and poses a significant pollution risk due to large residual amounts, this invention provides a method for inhibiting the formation of NDMA during the ozone treatment of UDMH wastewater.

[0007] The concept of this invention:

[0008] Unsymmetrical dimethylhydrazine (UDMH) reacts rapidly with ozone, but the reaction readily produces nitrosodimethylamine (NDM), which is difficult to degrade once formed. Therefore, controlling the reaction at its source is more efficient. In the gas phase reaction, UDMH mainly generates NDM through the oxidation of methyl groups to a metahydrazone intermediate. However, how to control the formation of NDM in an ozone system within an aqueous environment when treating UDMH wastewater remains unclear.

[0009] To address the current problems in ozone treatment of unsymmetrical dimethylhydrazine (UDMH) wastewater, this invention first investigated the effects of ozone dosage and pH value on the formation of nitrosodimethylamine during the treatment of medium-to-high concentration (50-100 mg / L) UDMH wastewater, as detailed below:

[0010] I. Impact of Ozone Dosage

[0011] Three portions of unsymmetrical dimethylhydrazine (UDMH) wastewater with a concentration of 100 mg / L were prepared. After introducing ozone at different concentrations (i.e., different ozone dosages), samples were taken at different time periods under neutral pH conditions. The content of nitrosodimethylamine was determined by high performance liquid chromatography with ultraviolet light as the detector, and the content of UDMH was determined by visible spectrophotometry. The results are shown in Figures 1 and 2.

[0012] Experimental results show that with the increase of ozone dosage, the degradation efficiency of unsymmetrical dimethylhydrazine (UDMH) increases, while the amount of nitrosodimethylamine (NDMA) generated increases. When the ozone dosage is 8 times the theoretical ozone dosage for complete degradation of UDMH, the removal rate of UDMH can reach 60%, while the generation rate of NDMA is as high as 50%. In subsequent reaction processes, the degradation efficiency of NDMA is slow. It is evident that the reaction between UDMH and ozone generates a large amount of NDMA, and once NDMA is generated, it is difficult to remove.

[0013] II. Effect of pH value

[0014] Based on the theoretical ozone dosage for complete degradation of unsymmetrical dimethylhydrazine (UDMH), eight times the amount of ozone was introduced into the UDMH wastewater. Dilute sulfuric acid and sodium hydroxide solutions were added to adjust the pH to 4, 7, and 9, respectively, and the concentration of UDMH in the wastewater was 100 mg / L. The reaction was stirred, and samples were taken at different time points. Nitrosaminoglycans were determined by high-performance liquid chromatography with ultraviolet light as the detector, and UDMH was determined by visible spectrophotometry. The results are shown in Figure 3.

[0015] Experimental results showed that in an environment with pH=4, the concentration of nitrosodimethylamine reached 67.1 mg / L after 1 hour of reaction; in an environment with pH=7, this concentration decreased to 30.0 mg / L; and when the pH was further increased to 9, the concentration of nitrosodimethylamine was only 2.942 mg / L. It can be seen that pH has a significant impact on the amount of nitrosodimethylamine formed, with the formation rate significantly higher in acidic environments than in neutral and alkaline environments. Therefore, alkaline conditions can effectively inhibit the formation of nitrosodimethylamine.

[0016] In summary, increasing the amount of ozone added can increase the degradation efficiency of unsymmetrical dimethylhydrazine, but it will also increase the amount of nitrosodimethylamine generated. As the pH value increases during ozone treatment, the proportion of unsymmetrical dimethylhydrazine converted into nitrosodimethylamine decreases significantly.

[0017] Therefore, this application aims to create an alkaline environment that can significantly reduce the conversion rate of nitrosodimethylamine and to increase the amount of ozone added several times over.

[0018] To achieve the above objectives, the technical solution provided by this invention is:

[0019] First, this invention provides the application of manganese sulfate as a catalyst in suppressing the formation of nitrosodimethylamine during ozone treatment of unsymmetrical dimethylhydrazine wastewater.

[0020] Secondly, this invention provides a method for suppressing the formation of nitrosodimethylamine during ozone treatment of unsymmetrical dimethylhydrazine wastewater, characterized by the following steps:

[0021] 1) Control the concentration of unsymmetrical dimethylhydrazine in the wastewater at 80mg / L-100mg / L (the treatment effect is better if the concentration of unsymmetrical dimethylhydrazine in the wastewater is within this range), then add the catalytic amount of manganese sulfate and stir evenly;

[0022] 2) Adjust the pH of the wastewater from step 1) to 7-9, and introduce ozone into the wastewater at a level 6-8 times the theoretical ozone dosage for complete degradation of unsymmetrical dimethylhydrazine (UDMH). Stir the reaction. During the reaction, when the ozone content drops to 1 / 5 of the initial ozone content, continue introducing ozone into the wastewater until it reaches 6-8 times the theoretical ozone dosage for complete degradation of UDMH; continue until all byproducts in the wastewater are removed. There is no strict order between adjusting the wastewater pH and introducing the initial ozone in this step. Adjusting the pH of the wastewater within the first hour of the reaction will inhibit the formation of nitrosodimethylamine.

[0023] Furthermore, it also includes: 3) adjusting the pH of the reacted solution to neutral so that wastewater can be tested and discharged normally.

[0024] Furthermore, in order to better inhibit the formation of nitrosodimethylamine, in step 2), the pH value of the wastewater is adjusted to 9, and the ozone dosage is 8 times the theoretical ozone dosage for the complete degradation of unsymmetrical dimethylhydrazine.

[0025] Furthermore, in step 1), the amount of manganese sulfate added to the wastewater is 0.3-0.4% of the unsymmetrical dimethylhydrazine content.

[0026] Furthermore, in step 2), the reaction is stirred for 2-3 hours.

[0027] Furthermore, sodium hydroxide is used to adjust the pH value in both steps 2) and 3).

[0028] The principle of this invention:

[0029] The alkaline environment created by this invention generates a large number of hydroxyl radicals. Compared to ozone, unsymmetrical dimethylhydrazine (UDMH) is less likely to react with hydroxyl radicals to form nitrosodimethylamine. A competitive relationship is formed between hydroxyl radicals and ozone, where UDMH is more likely to react. With the catalytic support of divalent manganese ions, hydroxyl radicals block the possible reaction between ozone and UDMH at the source. Simultaneously, amino groups are less prone to protonation under alkaline conditions and readily react with hydroxyl radicals. Hydroxyl radicals easily remove hydrogen atoms from amino groups to form diazene ((CH3)2N=N). Diazene readily couples with substances such as tetramethyltetraazene. Tetramethyltetraazene is less likely to form nitrosodimethylamine under ozone conditions, thus inhibiting the formation of nitrosodimethylamine during ozone treatment of UDMH wastewater at the source.

[0030] Advantages of this invention:

[0031] 1. The method of this invention can effectively remove unsymmetrical dimethylhydrazine (100%) and other toxic byproducts (metanehydrazone, cyanide, etc.).

[0032] 2. The method of this invention can effectively suppress the formation of nitrosodimethylamine in the ozone system (≤0.3%).

[0033] 3. The method of this invention can achieve low-cost control of nitrosodimethylamine pollution at room temperature, and the operation is extremely simple and easy to promote. Attached Figure Description

[0034] Figure 1 shows the changes in unsymmetrical dimethylhydrazine (UDMH) content under different ozone dosages;

[0035] Figure 2 shows the amount of nitrosodimethylamine generated under different ozone dosages;

[0036] Figure 3 shows the amount of NDMA generated in different pH environments (8 times the amount of ozone added).

[0037] Figure 4 shows Mn 2+ / O3 treatment of unsymmetrical dimethylhydrazine wastewater and changes in unsymmetrical dimethylhydrazine and nitrosodimethylamine content;

[0038] Figure 5 shows Mn 2+ / O3 treatment of unsymmetrical dimethylhydrazine wastewater gas chromatographic analysis of unsymmetrical dimethylhydrazine byproducts. Detailed Implementation

[0039] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0040] This invention provides a method for suppressing the formation of nitrosodimethylamine during ozone treatment of unsymmetrical dimethylhydrazine wastewater, specifically comprising the following steps:

[0041] Step 1: Control the concentration of unsymmetrical dimethylhydrazine in the wastewater to 80 mg / L-100 mg / L, then add manganese sulfate (chemically pure) and stir evenly; wherein, the amount of manganese sulfate added to the wastewater is 0.3-0.4% of the unsymmetrical dimethylhydrazine content;

[0042] Step 2: Adjust the pH of the wastewater from Step 1) to 7-9 using sodium hydroxide. Then, introduce ozone into the wastewater at a dosage 6-8 times the theoretical ozone dosage for complete degradation of unsymmetrical dimethylhydrazine (UDMH). Stir the reaction. During the reaction, when the ozone content drops to 1 / 5 of the initial ozone content, continue introducing ozone into the wastewater until it reaches 6-8 times the theoretical ozone dosage for complete degradation of UDMH, until all byproducts in the wastewater are removed. Ozone is consumed rapidly during the treatment process, therefore intermittent continuous ozone introduction is necessary. The interval should be controlled according to the ozone generation rate.

[0043] Step 3: After all byproducts in the wastewater have been removed, add sodium hydroxide to adjust the solution to near neutral, so that it can be tested to see if it meets the discharge standards;

[0044] Step 4: Gas chromatography and high-performance liquid chromatography (HPLC) are used for detection. If the residual amount of nitrosodimethylamine is not higher than 0.3%, it meets the relevant emission standards. The gas chromatography detection conditions are: injection port temperature 200℃, chromatographic column DB-225S, initial temperature 35℃, holding time 5 min, temperature ramped to 150℃ at a rate of 10℃ / mins, and split ratio 1:1.

[0045] Example 1

[0046] To prepare wastewater with a concentration of 100 mg / L of unsymmetrical dimethylhydrazine, add a catalytic amount of chemically pure manganese sulfate (0.3% of the unsymmetrical dimethylhydrazine content) and stir until homogeneous.

[0047] The pH of the wastewater from step 1) was adjusted to 9, and ozone at a level 8 times the theoretical ozone dosage for the complete degradation of unsymmetrical dimethylhydrazine was introduced into the wastewater. The reaction was stirred, and ozone was intermittently introduced every 1 hour until it reached 8 times the theoretical ozone dosage for the complete degradation of unsymmetrical dimethylhydrazine. Samples were taken at different time points. High performance liquid chromatography with ultraviolet light as a detector was used to determine nitrosodimethylamine, and visible spectrophotometry was used to determine unsymmetrical dimethylhydrazine. All products were analyzed by gas chromatography. The results are shown in Figures 4 and 5.

[0048] The results showed that after 3 hours of treatment, the removal rate of unsymmetrical dimethylhydrazine was close to 100%, which was basically completely removed. Under the action of divalent manganese ions, the product analysis in Figure 5 showed that the formation rate of nitrosodimethylamine was low (≤0.3%) during the reaction, and other by-products were also basically completely removed.

[0049] Example 2

[0050] The difference from Example 1 is as follows:

[0051] In step 1, the concentration of unsymmetrical dimethylhydrazine in the wastewater is controlled at 80 mg / L.

[0052] Example 3

[0053] The difference from Example 2 is that:

[0054] In step 2, sodium hydroxide is used to adjust the pH of the wastewater from step 1 to 7.

[0055] Example 4

[0056] The difference from Example 1 is as follows:

[0057] In step 1, the concentration of unsymmetrical dimethylhydrazine in the wastewater is controlled at 90 mg / L.

[0058] In step 2, the pH of the wastewater from step 1) is adjusted to 8 using sodium hydroxide, and ozone at a dosage of 6 times the theoretical ozone dosage is introduced into the wastewater to completely degrade unsymmetrical dimethylhydrazine.

[0059] Tests on the wastewater treated in Examples 2-4 showed that the formation of nitrosodimethylamine during the ozone treatment of unsymmetrical dimethylhydrazine wastewater was suppressed at the source, thus meeting the emission standards.

[0060] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the scope of the technology disclosed in the present invention, and such modifications or substitutions should all be covered within the scope of protection of the present invention.

Claims

1. Application of manganese sulfate as a catalyst in suppressing the formation of nitrosodimethylamine during ozone treatment of unsymmetrical dimethylhydrazine wastewater.

2. A method for suppressing the formation of nitrosodimethylamine during ozone treatment of unsymmetrical dimethylhydrazine wastewater, characterized in that, Includes the following steps: 1) Control the concentration of unsymmetrical dimethylhydrazine in the wastewater at 80mg / L-100mg / L, then add a catalytic amount of manganese sulfate and stir evenly; 2) Adjust the pH of the wastewater in step 1) to 7-9, and introduce ozone into the wastewater at a dose 6-8 times the theoretical ozone dosage for complete degradation of unsymmetrical dimethylhydrazine, stirring the reaction. During the reaction, when the ozone content drops to 1 / 5 of the initial ozone content, continue to introduce ozone into the wastewater until it reaches 6-8 times the theoretical ozone dosage for complete degradation of unsymmetrical dimethylhydrazine, until all byproducts in the wastewater are removed.

3. The method according to claim 2, characterized in that, Also includes: 3) Adjust the pH of the solution after the reaction to neutral.

4. The method according to claim 2 or 3, characterized in that: In step 2), the pH of the wastewater is adjusted to 9, and the ozone dosage is 8 times the theoretical ozone dosage required for the complete degradation of unsymmetrical dimethylhydrazine.

5. The method according to claim 4, characterized in that: In step 1), the amount of manganese sulfate added to the wastewater is 0.3-0.4% of the unsymmetrical dimethylhydrazine content.

6. The method according to claim 5, characterized in that: In step 2), the reaction is stirred for 2-3 hours.

7. The method according to claim 6, characterized in that: Sodium hydroxide was used to adjust the pH value in both steps 2) and 3).

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